S500QL and S960QL are ultra-high-strength, quenched and tempered structural steel plates manufactured to the European standard EN 10025-6. The "QL" suffix specifies their delivery condition: Quenched (Q) and Tempered (T) with guaranteed impact toughness (L) at low temperatures (typically -40°C or -60°C). These grades are engineered for critical, highly stressed welded structures in extreme applications such as heavy-duty mobile cranes, high-capacity mining equipment, offshore support structures, and advanced military vehicles, where an optimal balance of exceptional strength, fracture toughness, and weldability is required.
Key Differences:
The defining distinction is their dramatic difference in strength. S500QL offers a minimum yield strength of 500 MPa, while S960QL provides a substantially higher yield strength of 960 MPa. This 92% strength increase places S960QL at the pinnacle of commercially available high-strength structural steels, enabling maximum weight reduction and ultimate load-bearing capacity in design.
Achieving this extreme strength while simultaneously meeting the stringent "QL" toughness requirements necessitates a fundamentally more advanced metallurgical approach for S960QL. Its chemical composition involves significantly higher levels of carbon, manganese, and alloying elements such as chromium, nickel, molybdenum, and boron, processed under precisely controlled quenching and tempering. Consequently, S960QL has a vastly higher carbon equivalent (Ceq) and crack sensitivity index compared to S500QL. This results in exponentially greater fabrication complexity. Welding S960QL is exceptionally restrictive: it demands specially developed, ultra-high-strength and high-toughness consumables, meticulous control of very high preheating temperatures (often above 200°C), extremely low heat input, strict interpass temperature limits, and is almost always followed by mandatory post-weld heat treatment (PWHT) to mitigate hydrogen cracking and restore toughness in the heat-affected zone.
Chemical composition for S500QL steel plate (Heat Analysis Max%)
| Main chemical elements composition of S500QL steel plate | |||||||
| C | Si | Mn | P | S | N | B | Cr |
| 0.20 | 0.80 | 1.70 | 0.020 | 0.010 | 0.015 | 0.005 | 1.50 |
| Cu | Mo | Nb | Ni | Ti | V | Zr | |
| 0.50 | 0.70 | 0.06 | 2.0 | 0.05 | 0.12 | 0.15 | |
Chemical composition for S960QL steel plate (Heat Analysis Max%)
| Grade | C % | Si % | Mn % | P % | S % | N % | B % | Cr % |
| S960QL | 0.200 | 0.800 | 1.700 | 0.020 | 0.010 | 0.015 | 0.005 | 1.500 |
| Cu % | Mo % | Nb % | Ni % | Ti % | V % | Zr % | ||
| 0.500 | 0.700 | 0.060 | 2.000 | 0.050 | 0.120 | 0.150 |
Mechnical property for S500QL steel plate:
| Thickness (mm) | |||
| S500QL | ≥ 3 ≤ 50 | > 50 ≤ 100 | > 100 |
| Yield strength (≥Mpa) | 500 | 480 | 440 |
| Tensile strength (Mpa) | 590-770 | 590-770 | 540-720 |
Mechnical property for S960QL steel plate:
| Grade | Thickness(mm) | Min Yield (Mpa) | Tensile(MPa) | Elongation (%) | Min Impact Energy | |
| S960QL | 8mm-50mm | Min 960Mpa | 980-1150Mpa | 10% | -40 | Min 30J |
| 51mm-100mm | Min 910Mpa | 920-1000Mpa | 10% | -40 | Min 30J | |
| 101mm-150mm | Min 860Mpa | 870-980Mpa | 10% | -40 | Min 30J |
